The present invention relates to a method for forming perforations in bar-shape articles using laser rays.
The present invention finds particularly advantageous application in the field of the production of smoking articles, in particular cigarettes, to which the following discussion will make specific reference without loss of generality thereby.
In the field of cigarette manufacture it is known to make so-called "ventilated" cigarettes, that is to say cigarettes having a plurality of holes in the region of the filter, for permitting the smoker to inhale, together with the smoke, a percentage of external air, with the double advantage of diluting the inhaled smoke and reducing the temperature, and, therefore, the content of harmful elements.
In the past, needle devices have been used to make ventilated cigarettes, the efficiency of which needle devices has become less and less with the increase in the productive capacity of cigarette making machines. In fact, if associated with a relatively high speed cigarette making machine the said needle devices wear out in a relatively short time thus causing frequent interruptions in the productive cycle.
For the reasons explained above the said needle devices have recently been replaced, when possible, by laser ray perforator devices which have been made in one of two different constructional arrangements. In the first of these two constructional arrangements mentioned above a pulsed beam of laser rays is emitted by a fixed laser generator and directed onto a cigarette to be pierced. This latter, during the piercing operation, is rolled between two facing surfaces in such a way as to turn on itself. Consequently, the holes formed on it are distributed in a substantially uniform manner along at least one circumference.
In the other of the two above mentioned constructional arrangements a laser generator of high power is used, which for piercing each cigarette emits a single beam which is broken down by fixed reflectors into a plurality of beams the number of which is equal to the number of holes to be formed. In this case the holes in each cigarette are made simultaneously without it being necessary to make it turn about its own axis.
Both of the above described known constructional arrangements have significant disadvantages which make their practical application problematical. In fact, the rolling of cigarettes required by the first said constructional arrangement is particularly damaging in that the cigarettes have immediately previously already been "softened" following a first rolling performed during the operations for connection of the filter, and the further rolling to perform the piercing certainly involves a partial emptying of the cigarettes. The second of the two above described constructional arrangements is, on the other hand, difficult to put into practice for purely economic reasons given the high power and therefore, the high cost of the laser generator which must be used.